In U.S. Pat. No. 4,604,111, a particulate contamination control method and filtration device is disclosed. This patent relates to the serious dangers associated with persons breathing particulate contaminated air. The invention is useful for protecting the outside environment and the individuals working in a highly contaminated area such as occurs when asbestos coatings are removed inside a building structure.
Asbestos fibers fall into the generic classification of hazardous particulate and are a well known carcinogenic hazard to humans and animals. Typical environmental standards refer to fibers that are 5 microns or greater in length with an aspect ratio of 3 to 1 or greater. The average asbestos fiber is about 0.1 micron in diameter. It is now accepted that the thinner fibers are the most dangerous threat to human health. The asbestos fibers, in particular those that are thinner and shorter, remain airborne for considerable lengths of time and contaminate large volumes of air to form a substantial hazard to the environment and to the persons working or living in the area.
U.S. Pat. No. 4,604,111 provides a system and method of containing, lowering, and essentially eliminating the danger of asbestos inhalation by workers in a building in which asbestos fibers are generated at extremely high levels. Asbestos fibers are prevented from being released into the outside environment during an unforseen accident such as a leak through a damaged film barrier and by a flap seal which seals an inlet to a contaminated work area through which workers pass to gain entrance to and exit from the work area.
The flap seal is formed in a plastic wall defining the work area. The "flap seal" includes a two foot by five foot opening about a foot off the floor in a sheet of plastic film, such as polyethylene, plasticized polyvinyl chloride or the like, sealed across an existing door frame of the work area. A polyethylene sheet is sealed across a door frame with an opening cut through the film. The flap is larger in all dimensions than the opening of the same film, is attached to the door frame above the opening and hangs over the full length of the opening such that air and the workers may pass into the work area through the opening, pushing the flap inwardly. However, the configuration is such that once the air flow ceases and positive air pressure develops in the enclosure, the flap falls into place and air is prevented from escaping in the opposite direction to the environment outside of the work room.
In the U.S. Pat. No. 4,604,111, the flap seal is designed to seal the inlet into the contaminated work area. This arrangement has proved very effective in preventing escape of asbestos fibers in the event of loss of negative pressure. However, other factors need to be considered in designing a combined entranceway and exit from a contaminated work area.
In U.S. Pat. No. 4,818,970, a fire condition detection and control system for air moving and filtering units is disclosed. The fire condition detection and control system is for use with air moving and filtering units such as those disclosed in U.S. Pat. No. 4,604,111. The fire condition detection and control system includes one or more remote fire condition detection units, which sense heat or smoke and, upon such sensing, transmit a signal indicative of an alarm condition to one or more air moving and filtering units located within a containment enclosure. The transmission is by wireless radio frequency transmission and/or a wired transmission line or cable. The air moving and filtering unit detects the alarm condition and disconnects power to the blower motor of the air moving and filtering unit. The receiver and control circuitry may be integral with the air moving and filtering unit, or may be part of a separate control unit that plugs into conventional air moving and filtering units.